Your body and mine: a neuropsychological perspective

The concept of "shared representations" suggests the existence of a common representation network between self and other. Strong support for this theory is derived from the discovery in the monkey of a population of neurons, which encode object-directed actions performed by oneself and by others. In the human, the issue of "shared representations" has been raised in brain-damaged studies, in particular in the setting of "pointing to body parts" disorders. According to the dominant view, body part designation engages a shared representation system, which encodes the visuospatial characteristics of both one's own body and the bodies of other individuals. However, the recent observation of two patients, JR and AP, with dissociated performance in pointing to body parts leads to question this model. JR presented a deficit in pointing to his own body parts, while his capacity to point to the body parts of other persons was not altered. AP exhibited the reverse pattern of impairment. Lesion study indicated a putative area of dysfunction setting in the left superior parietal lobule (SPL) in JR, and in the left inferior parietal lobule (IPL) in AP. This double dissociation, along with two subsequent neuroimaging studies, suggests that the left SPL and IPL participate in the building of differential representations between oneself and other individuals.